1. Field of the Invention
The present invention relates to a sound signal processing apparatus used to separate speech from an input sound signal containing ambient sound such as ambient noise, background noise, etc., and speech and used to attenuate ambient sound so as to accentuate speech, and relates to a degree of speech computation method for use with the sound signal processing apparatus.
2. Description of the Related Art
In applications such as mobile phones and speech recognition, it is desirably to suppress noise such as ambient noise and background noise, which is contained in a picked-up sound signal or an audible signal in order to accentuate speech components and to separate noise and speech.
As such, a conventional technology for separating speech and noise, as disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 2000-81900 and 8-79897, a method for separating speech and noise from differences in sound signals received by each microphone by using a plurality of microphones is known. Furthermore, as disclosed in Japanese Unexamined Patent Application Publication Nos. 2001-42886 and 2000-222000, a method of learning ambient sound at the time of a particular timing is known. In, for example, Japanese Unexamined Patent Application Publication No. 2003-70097, a method is disclosed in which the minimum average amplitude value in a fixed period is assumed as noise, and a determination as to ambient sound and speech is made based on the magnitude relationship with that value.
As recognized by the present inventors, the above-described conventional technologies have the following problems.
In the case of the technologies disclosed in Japanese Unexamined Patent Application Publication Nos. 2000-81900 and 8-79897, in which a plurality of microphones are used, it is required that the microphones be at a minimum fixed spacing or more. In the case of a directional microphone, the direction needs to be changed in accordance with the movement of a target.
In the case of the technologies disclosed in Japanese Unexamined Patent Application Publication Nos. 2001-42886 and 2000-222000, in which ambient sound is learned, ambient sound of a time that is necessary and sufficient for learning is required, and the technologies lack general versatility.
In the case of the technology disclosed in Japanese Unexamined Patent Application Publication No. 2003-70097, it is not possible to cope with noise of a large amplitude, and a determination is difficult when the entirety of a fixed period is only speech or only ambient sound.